An inflatable vehicle occupant protection device, such as an air bag, is deployed upon the occurrence of a vehicle crash. The air bag is part of a vehicle occupant protection apparatus which further includes a crash sensor and an inflator. The crash sensor senses vehicle conditions that indicate the occurrence of a crash. When the crash sensor senses a crash-indicating condition of at least a predetermined threshold level, the inflator is actuated. The inflator then emits inflation fluid which inflates the air bag into the vehicle occupant compartment. When the air bag is deployed in this manner, it helps to protect an occupant of the vehicle from a forceful impact with parts of the vehicle as a result of the crash.
The manner in which the air bag affects movement of the vehicle occupant can be influenced by factors such as the force with which the occupant moves against the air bag and the pressure of the inflation fluid in the air bag. Those factors, in turn, can be influenced by vehicle conditions such as the severity of the crash, and/or by vehicle occupant conditions such as the size, weight and position of the occupant.